Variable frequency reflex klystrons



April 7, 1959 'J. BERNIER VARIABLE FREQUENCY REFLEX KLYSTRONS 2 Sheets-Sheet 1 Filed March 51, 1955 INVENTORS Jean BERNIER YEOU TA BY ATTORNE w .W, W, a a w\ 4 .M. w 1, .9 H

April 7, 1959 J. BERNIER ETAL Filed March 3.1, 1955 2 sheets-sheet 2 Ida INVENTOR S Jean BERNIER U TA 647 ATTORNE United States Patent VARIABLE FREQUENCY REFLEX KLYSTRONS Jean Bernier and Ta Yeou, Paris, France, assignors to Compagnie Generale de Telegraphic Sans Fil, a corporation of France Application March 31, 1955, Serial No. 498,399 Claims priority, application France April 6, 1 954 2 Claims. (Cl. 3155.22)

The invention relates to reflex klystrons and more particularly to variable frequency reflex klystrons for producing microwave energy in the millimeter range.

The variable frequency reflex klystrons used in this wave band, generally exhibit power gaps in respect of certain frequencies, that is considerable drops in power.

These disadvantages are mainly due to the mechanical tuning devices in klystrons of this type. Generally these devices control simultaneously the displacement of the reflector and the deformation of a deformable wall of the cavity resonator. Now, it is diflicult to exert a force for ensuring such a deformation, which is strictly normal to the surface of the deformable wall at every point. The resultant irregular deformation results in variations in the coupling between the cavity and the load.

' Further, the mechanical devices used in the microwave range are generally fully enclosed in the envelope of the tube so as better to withstand the vibrations, which have considerable effect on the operation of the klystrons of this type. These devices are therefore controlled from without the tube for example, by bimetallic strip devices which are electrically heated. Their reliability is not very satisfactory.

The present invention has as its object to. provide a variable frequency reflex klystron, the tuning device of which is entirely mechanical, wholly enclosed in the envelope of the tube and is adapted to ensure with high accuracy and perfect fidelity both small deformations of the tuning wall of the cavity resonator and small displacements of the reflector, the directions of the forces effecting these displacements and deformations always being parallel to the axis of the tube.

According to the invention, the microwave klystron is characterized by a tuning device, the essential elements of which are:

(a) A flexible diaphragm which is integral with the envelope of the tube and means outside this envelope to ensure the deformation of this diaphragm.

(b) Disposed in the envelope of the tube: a cavity resonator having a flexible wall, a displaceable reflector support, said flexible wall permitting tuning of the resonant frequency of the cavity; the flexible wall and reflector support being welded together.

(0) Means inside the tube to guide the movements of the reflector support along a linear axis normal to the flexible wall of the cavity.

(d) Means permitting the transmission of the forces applied on the flexible diaphragm to the reflector support so as to displace the latter in a first direction, these means 2,881,351 Patented Apr. 7, 1959 Figure 1 is a diagrammatic illustration of the principle of the tuning device of the invention.

Figure 2 is an axial sectional view of an embodiment of the reflex klystron of the invention.

Figures 3 to 11 are perspective views of certain elements shown in Figure 2.

Fig. 1 shows the restonating cavity 110 of the klystron which comprises two walls 30 and 40 of revolution about a common axis and a glass window 110a for extracting energy from the cavity. The wall 40 is flexible and permits the cavity to be tuned. This wall is soldered to a metallic member 60 in the form of a hollow tube coaxial with the cavity. This member 60 is rendered unitary with the reflector electrode 70 by an insulating washer 150 serving as a support for the latter reflector. The latter comprises a metallic stem coaxial with the cavity. The member 60 is slidable in a guide 50, the latter having the shape of a body of revolution and being coaxial with the above-mentioned elements. Two shoulders 510 and 520 are formed in this guide 50.

The member 60 has two shoulders 600 and 610 which are adapted to abut the shoulders 510 and 520 and hence limit the movements of the member 60.

The guide 50 is also soldered at its lower part to the diaphragm 40. Its upper part' is soldered to a glass wall 700 in the form of a tube of revolution. Members 50 and 700 are parts of the envelope of the tube. This envelope is closed at its upper end by a flexible diaphragm 80. The deformations of this diaphragm are controlled by a knob 90. This diaphragm bears against a domeshaped member 140 integral with the reflector support.

The member 60 has an abutment 630. A compression spring 100, is disposed between the abutments 630 and 510. A connection 210 applies to the reflector the required voltage.

The system operates in the following manner: If the knob exerts a downward force on the diaphragm 80, the unit 140 and 60 is displaced downwardly and owing to the action of the guide 50, in a direction exactly parallel to the axis of the tube. The reflector 70 is thus lowered and the wall 40 is simultaneously deformed by the action of reflector support 60. The forces exerted on the wall 40 are always in the direction parallel to the axis of the tube.

When the knob 90 is upwardly displaced, the spring maintains the contact between the dome-shaped member and the diaphragm 80. The forces transmitted by the spring 100 remain in direction of the axis of the tube but act upwardly.

Figure 2 is an axial sectional view of a klystron embodying the tuning device of the invention and having a structure of revolution. A feature of this klystron is that all its component parts are coaxial with a cylinder 2 of Kovar. All the other metallic parts of the klystron are of Kovar except for those specially mentioned. The cylinder 2 is shown in perspective in Fig. 3 on a reduced scale. Two vglass windows Zaf'Z'are formed in its periphery for the purpose of power output. Mounted in this cylinder 2 is a member 3 (Fig. 4) in which are formed a central aperture Sa and peripheral apertures 312 The central aperture 3a provides a passageway for the electron beam. The diflerent parts of the tube are interconnected by way of the peripheral apertures 311 The member 3 is covered with a pure silver diaphragm 3a forming the lower wall of the resonant cavity 1 of the tube. Another member 4 seen in Figure 5, comprises adjacent its periphery, several apertures 4b the purpose of which will be explained hereunder, and in its central portion a system of claws 4b. Soldered to this member is another silver diaphragm 4a forming the upper wall of the cavity of the tube. This diaphragm (Figure 6) comprises a series of annular square-sectioned undulations 4c which match the U.H.F. impedance of the central part It: to the impedance of peripheral part 117 of the cavity 1. This member 4a is the flexible wall by means of which the cavity is tuned. The cavity is provided with re-entrant portions at both cavity walls 3a and 4a.

The wall 4a has a central aperture 4:2 for the passage of the electron beam. This aperture is formed after the flexible wall 4a has been soldered to the member 4 so as to ensure that this aperture remains in the axis of the tube. Disposed between the members 3a and 4a are the abovementioned power outputs 2a provided on the cylinder 2.

A member (Figure 7) riveted to the member 4 through peripheral holes 5b; which correspond to holes 4b comprises on its upper end an arrangement of claws 5b which correspond to the claws 4b and are in alignment with the latter when the members 4 and 5 are assembled.

Some of the holes 4b and Sb constitute apertures of communication between the several parts of the tube. The member 5 also has a guiding stud 5c.

A member 11 provided with holes 11b is disposed on the upper end of the member 5 and acts as an abutment.

Slidable between the claws 5b and 4b is a portion 60 of a cylindrical member 6 (Figure 8). The latter is provided with an axial bore and at its lower end 6d is welded to the central portion of the flexible wall 4a, the deformation of which it controls. The member 6 has two peripheral shoulders or abutments 6061, identified in Figure 8, which abut respectively on the members 5-4, and therefore, limit the longitudinal movement of this member. Also, a key slot 6g formed in the member 6 and engaged by the stud 5c prevents this member from rotating about its axis.

Screwed. on the member 6 is a nut any rotations of this nut. The member 6, through the medium of a dielectric member such as a glass bead 15, supports the reflector 7 of the klystron.

The reflector is centered and set at the correct distance from the flexible wall 4a very easily by means of a jig when welding the glass bead to the reflector support.

Disposed between the abutment 11 and the nut 12 is a compression spring which upwardly urges the reflector support 6 and the central portion of diaphragm 4a.

Welded to the member 2 and defining part of the evacuated cylindrical envelope are a lower glass cylinder closed at its lower end by a rigid base and an upper tubular glass cylinder 80 closed in its upper end by the flexible diaphragm 8. The central portion of the latter bears against the dome-shaped member 14. A knob 9 brazed on diaphragm 8 is used in downwardly displacing the unit 67. The arrangement shown in Fig. 1 will be recognized.

An. insulated passageway 26 is provided in domeshaped member 14 for supplying the required voltage to the reflector.

Likewise, the electronic gun of the tube is disposed centrally of the member 2. The means for obtaining this comprises a hollow cylinder 19 coaxial with and rig- 12 rigid with a dome-shaped member 14. A locking screw 13 prevents idly secured to the member 2 by stays such as 27 and 28. The position of the unit comprising the cathode 17 and the Wehnelt cylinder 18a, 18b relative to cylinder 19 is governed by a spring 23 and two mica washers 21 and 21 (Figs. 910). The Wehnelt cylinder comprises two elements 18a and 18b (Fig. 11); element 18a is removable to allow assembly of the washer 21. The element 18a has been machine turned and its inner shape is formed of two coaxial adjoining cones which ensure perfect reproduction of the parts of the Wehnelt cylinder. All the elements located on the side of the electron gun are securely held in position relative to the body of the klystron by a nut 25. An arrangement of distance pieces and cast silica washers hold the cathode in position relative to the Wehnelt cylinder.

The anode 20 is fitted in the cylinder 19.

The position of all the elements of the tube is thus fixed in relation to the cylinder 2. It should be noted that all the elements of the tube (except for the walls of the cavity resonator of silver and the springs of molybdenum), are made preferably of the same material (Kovar), so as to avoid any distortion due to difierences of expansion when being stoved, Kovar having practically the same coefiicient of expansion as glass. The silver diaphragms of the cavity resonator are electrically welded to massive elements of Kovar.

Further, it will be observed that the windows 2a close the outer part of the cavity and do not affect its Q factor.

What we claim is:

l. A reflex klystron tube for generating millimeter waves comprising an evacuated envelope and having supported within the envelope a cathode, a Wehnelt cylinder, an accelerating anode, a cavity resonator having a flexible wall and a rigid wall, and a displaceable reflector electrode, means for simultaneously deforming said flexible wall and for displacing said reflector along a predetermined linear axis to vary the operating frequency of the tube, said means comprising: a deformable diaphragm closing said envelope at one end thereof, means exterior of said envelope for displacing at least a part of said diaphragm in a predetermined direction, a support for said reflector electrode connected to said flexible wall within said envelope and means providing a punctual contact between said support and said part of said diaphragm for displacing said support along said predetermined axis in response to movement of said part in said predetermined direction, means within said envelope for guiding said support for movement only along said axis, means interior of said envelope comprising a spring for urging said support in the direction toward said diaphragm, and means for limiting the amplitude of displacement of said support along said axis.

2. A variable frequency reflex klystron oscillator tube for generating millimeter waves comprising an evacuated cylindrical envelope, having an axis and closed at its two ends by a rigid base and a flexible diaphragm, respectively, said envelope including two glass cylinders and one metallic cylinder disposed between and tightly fixed to said glass cylinders, said tube comprising within said envelope, a re-entrant cavity resonator disposed within said metal cylinder, rigidly fixed thereto and provided with a deformable wall at the side of said resonator nearest said flexible diaphragm, an electron gun disposed between said cavity and said rigid base and rigidly fixed to said metal cylinder for emitting an electron beam along said axis, a guide supported by said metal cylinder and rigidly fixed thereto, a movable hollow cylinder attached by one of its ends to said deformable wall and having a portion slidably disposed within said guide, a dome shaped cap adjacent said flexible diaphragm and fixed to the other end of said movable cylinder, a dielectric member supported by said hollow cylinder and rigidly fixed thereto, a metallic stem disposed along said axis within said hollow cylinder and rigidly fixed near one of its ends to said dielectric member,

.5 a reflector electrode disposed near said cavity and fixed to the other end of said stem, a spring acting on said movable cylinder and disposed outside of said guide for urging said movable cylinder toward said flexible diaphragm, abutments disposed in said guide for limiting longitudinal displacements of said movable cylinder, and a stud fixed to said guide and engaged in a slot provided in said movable cylinder for preventing rotational movement of the latter, and means outside of said envelope for exerting pressures on said dome-shaped cap through said flexible diaphragm for longitudinally moving said movable cylinder, thereby simultaneously displacing said 6 reflector electrode relative said cavity and varying the position of said deformable Wall for achieving frequency tuning.

References Cited in the file of this patent UNITED STATES PATENTS 2,411,912 Vance Dec. 3, 1946 2,508,141 Broadway et al. May 16, 1950 2,508,346 Laflerty May 16, 1950 10 2,719,246 Goddard Sept. 27, 1955 FOREIGN PATENTS 606,802 Great Britain Aug. 20, 1948 

